坤（张东健 饰）是一名技艺精湛的冷血杀手，效力于黑社会组织，深受上司的信赖。然而，一段不堪回首的往事使他生活在愧疚之中，对自己一直以来从事的行业亦产生了疑惑和动摇，就在此时，组织派给了他一个十分重要的任务，命他前往韩国，刺杀名为崔木景（金敏喜 饰）的女子。 　　崔木景是一个悲剧般的女人，一场意外夺走了她的丈夫和孩子的性命，失去了生命中的挚爱，这位悲伤的妻子和母亲，终日沉浸在绝望之中，只能依赖酒精和药物度日，不仅如此，她还得照料患有阿兹海默症的母亲。当坤出现在崔木景的面前，他的身份不仅仅只是一个想要夺取她性命的杀手，女儿的死令崔木景的心中充满了疑问，而答案就在坤的手中。Abandoned by his mother shortly after immigrating to America, Gon is raised by the mafia and grows up to become a cold-blooded hit-man. Though usually flawless in taking out his targets, Gon makes a terrible mistake of killing an innocent young girl. A flood of guilt takes over his life and the situation becomes worse when his boss assigns him the job of killing the young girl's mother. Gon's new target, Mogyeong, is a risk manager at an investment firm and has buried herself in work to bury her grief. She is completely unaware of her role at the heart of a dangerous conspiracy. Finally, she meets the man who wants to tell her the truth behind the death of her child.